There are 2 more common thread sizes in the world of lighting, 10mm and 1/2″ (12.7mm) approx. To find out what one you need is simple, there should be a thread that’s sticking out of your lamp fitting where the lampholder screws onto, you simply need to measure the outside diameter of that thread, After removing the lampholder.

10mm is generally used on modern lights and would be used if creating a new light fitting, whereas 1/2″ is found on older units such as floor standing and table lamps.

• 10mm Pitch is 1mm (Fine Thread)
• 1/2″ Pitch is 26 TPI (Turns per Inch)

If you cannot gain access to the male thread sticking out, and you only have the thread on the lampholder to measure, then the sizes will be as follows:

• 10mm Thread – 8.8mm Approx.
• 1/2″ Thread – 12mm Approx.

There are many other threads on the market depending on the origin of the lamp maker.

In Metric, there is:

• 8mm
• 13mm – (not to be confused with 1/2″ which is 12.7mm) They will kind of screw together, but due to pitches being different they will bind eventually.

And Imperial, there are a whole host of other size:

• 5/8″
• 5/16″
• 3/8″
• 1/4″ IP (American Thread)
• 1/8″ IP (American Thread)

We have a range of reucders/enlargers hat cover the more common sizes mentioned above, view our range here